Bay Geometry Research Articles

Oceanographic and climatic influences on Trooz Glacier, Antarctica during the Holocene

To evaluate the significance of recent widespread glacial recession in the Antarctic Peninsula, it is imperative to extend the limited instrumented record of glacier change with long sedimentary archives of the Holocene. Reconstructing glacial histories that capture the variability of environments in the Antarctic Peninsula will enable better constraint of ocean and climate forcings on regional glacial stability. Two sediment cores are analyzed from the 2007 RV/IB N.B. Palmer cruise to Collins Bay, the embayment immediately offshore Trooz Glacier on the Graham Land coast, and provide an archive to test controls on long-term stability of outlet glaciers in an open bay setting. Radiocarbon and Lead-210 (a short-lived radioisotope) age-depth models provide a timeline for Trooz Glacier behavior and associated oceanographic changes over the last 10,000 years.Magnetic susceptibility, grain size, diatom assemblage, total organic carbon, nitrogen, and stable isotopes of organic carbon are utilized as proxies for changing glacial and ocean conditions. Outer Collins Bay deglaciated by ∼10000 cal yr B.P. Diatom abundance and organic content signal productivity increase during further glacial recession from ∼8900 to 6100 cal yr B.P., which coincided with upwelling of relatively warm Circumpolar Deep Water into the bay. High productivity, characterized by Thalassiosira antarctica-dominated diatom assemblages with prominence of Fragilariopsis kerguelensis, indicate open marine conditions with incursion of offshore currents into the bay from ∼6100 to 760 cal yr B.P. A sharp decrease in organic content, diatom abundance, and grain size indicate more sea ice and ice-tongue/ice-canopy advance from ∼760 to 240 cal yr B.P., when the floating ice canopy in outer Collins Bay retreated to near its present-day position and productivity increased. During the period of the 1950's to 1990's, Trooz Glacier was one of only two Antarctic Peninsula glaciers that advanced slightly. Over the Holocene, oceanographic forcing dominated the long-term stability of Trooz Glacier due to its open aspect, and it is unknown how Trooz Glacier will respond to continued influence of Circumpolar Deep Water in the future. Understanding ocean forcings on glacial stability, together with other local controls like drainage basin configuration and bay geometry, should help contextualize the modern retreat and improve prediction of glacial response to prevalent Circumpolar Deep Water circulation in this dynamic region.

Spatial patterns in wave signatures on beaches in estuaries and bays

Sandy beaches in estuaries and bays (BEBs) are ubiquitous around the world. While some are referred to as “low energy” beaches, there are large differences in wave climate due to fetch, swell exposure and shoreface morphology. In this study, wave-climate controls on BEB morphology are identified relative to bay geometry and focusing on the relative contributions of wind, ocean swell and infragravity waves to the wave signature of a BEB. We focus on two swash-aligned and two drift-aligned BEBs in an urbanized, semi-enclosed bay in SE Australia (Kamay/Botany Bay), with differences in proximity to the bay mouth, beach aspects and fetch, as well as different histories of storm erosion and recovery. Spectral analysis of local wave measurements (June 2018–January 2019) shows that wave signatures at all 4 BEBs are dominated by swell waves (>51%), followed by locally generated wind waves at 3 out of 4 BEBs (<43%), then infragravity waves (<35%). We identified five weather scenarios based on local wind speed/direction and resultant wind waves, combined with infragravity waves, and offshore swell wave conditions. BEBs close to the bay entrance are primarily controlled by swell waves, but at times even BEBs close to the entrance can be sheltered from swell waves depending on their incident angle. Conversely, BEBs farthest from the bay entrance (~8 km) alternated between periods where spectra were dominated by either wind waves or offshore swells. Infragravity waves were only important relative to wind waves and swell at the most sheltered BEBs, where there is limited fetch and swell dissipated over shallow areas. We also show that anthropogenic factors such as constructed revetments or groynes significantly alter wave signatures at BEBs in this bay. Thus, wave spectral signatures are highly variable across BEBs in the same bay and can represent a simple tool to study BEB morphodynamics including storm response and subsequent recovery.

The 1958 Lituya Bay tsunami – pre-event bathymetry reconstruction and 3D numerical modelling utilising the computational fluid dynamics software Flow-3D

Abstract. This study aims to test the capacity of Flow-3D regarding the simulation of a rockslide-generated impulse wave by evaluating the influences of the extent of the computational domain, the grid resolution, and the corresponding computation times on the accuracy of modelling results. A detailed analysis of the Lituya Bay tsunami event (1958, Alaska, maximum recorded run-up of 524 m a.s.l.) is presented. A focus is put on the tsunami formation and run-up in the impact area. Several simulations with a simplified bay geometry are performed in order to test the concept of a “denser fluid”, compared to the seawater in the bay, for the impacting rockslide material. Further, topographic and bathymetric surfaces of the impact area are set up. The observed maximum run-up can be reproduced using a uniform grid resolution of 5 m, where the wave overtops the hill crest facing the slide source and then flows diagonally down the slope. The model is extended along the entire bay to simulate the wave propagation. The tsunami trimline is well recreated when using (a) a uniform mesh size of 20 m or (b) a non-uniform mesh size of 15 m × 15 m × 10 m with a relative roughness of 2 m for the topographic surface. The trimline mainly results from the primary wave, and in some locations it also results from reflected waves. The denser fluid is a suitable and simple concept to recreate a sliding mass impacting a waterbody, in this case with maximum impact speed of ∼93 m s−1. The tsunami event and the related trimline are well reproduced using the 3D modelling approach with the density evaluation model available in Flow-3D.

Fluid–Structure Interactions on a Tunable Store in Complex Cavity Flow

Fluid–structure interactions were studied on a store with tunable structural natural frequencies in complex cavity flow. Different leading-edge geometries, doors, and internal inserts generated cavity pressure fields more representative of an actual aircraft bay. The store loading and response was characterized using point pressure and accelerometer measurements, while high-frequency pressure-sensitive paint captured the distribution of surface pressure. In the complex cavity, the store responded to the cavity resonant tones not only in the streamwise and wall-normal directions but also in the spanwise direction. That spanwise response to cavity tones was not observed in a simple rectangular cavity because the flow in the spanwise direction was uniform and in phase. This different behavior highlights the importance of using a representative bay geometry and internal store for the prediction of the structural response in a flight environment.

A parametric study of tsunami fission generation in a bay geometry based on numerical simulation

ABSTRACTTsunami fission generates short waves at the front face of tsunami and these short waves may expand the inundation area, increase the hydrodynamic forces exerted on structures, and amplify the damage to coastal communities. It is therefore important to understand to what extent the tsunami fission generates such short wave components under variable conditions for development of better tsunami disaster mitigation strategies and plannings. This study carried out numerical experiments to describe under which conditions the tsunami fission occurs in a bay. The experiments indicated that the amplification of the nearshore tsunami height induced by the narrowing bay geometry and the bay-scale resonance enhance the tsunami fission. Based on the computations, a parametric diagram for the occurrence of tsunami fission was proposed in terms of the tsunami properties, the effect of bay geometry and the bay resonance. The developed diagram was applied to Sendai, Ryori, Yoshihama, and Toni Bays, which were affected by the 2011 Tohoku Tsunami. The proposed diagram consistently explained the occurrence of tsunami fission in Sendai Bay and in Ryori Bay as observed in the video footage. The diagram also suggested that the tsunami fission would have occurred in Yoshihama Bay. A high-resolution numerical computation was performed to simulate the tsunami deformation in the Yoshihama Bay and Toni Bay based on a nonlinear dispersive wave model. The result supported the validity of the diagram in describing the generation of tsunami fission in Yoshihama Bay.

Impact of human interventions on tidal stream power: The case of Cádiz Bay

This work quantifies how human interventions can modify the tidal energy potential in a mesotidal estuary and if these variations can be used to increase the production of renewable energy at a highly altered bay. The analysis is applied to Cádiz Bay (Southern Spain), where important human interventions are developing, specifically a new port terminal and a 5 km long bridge. Due to these interventions, significant impacts on the bay hydrodynamics are expected. To assess the variations on the tidal energy resource after interventions, a three dimensional numerical model is used to obtain the bay hydrodynamics (Delft3D model). It was calibrated and validated against water levels and currents at tidal and sub-tidal scales using the results of two extensive field surveys. Two scenarios are defined, corresponding to the pre and post interventions situations. Results show that before interventions, only one area has the potential to locate a Tidal Energy Converter (TEC) array. However, after interventions a new area arise due to the increase of flow velocities induced by human modifications of the bay geometry. The energy potential is assessed for these two locations, and their efficiencies (potential energy per device) are obtained, indicating that after interventions the new TEC array is even more efficient than that of the pre interventions scenario, and an increase of 20% in the energy that can be potentially produced is obtained.

Potential Impacts of PCBs on Sediment Microbiomes in a Tropical Marine Environment

Within the tropical marine study site of Guánica Bay, Puerto Rico, polychlorinated biphenyls (PCBs) are subjected to coastal and oceanic currents coupled with marine microbial and geochemical processes. To evaluate these processes a hydrodynamic model was developed to simulate the transport of PCBs within nearshore and offshore marine areas of Guánica Bay. Material transport and circulation information from the model were matched with measurements from samples collected from within the bay. These samples, consisting of both intertidal and submerged sediments, were analyzed for physical characteristics (organic carbon, grain size, and mineralogy), microbial characteristics (target bacteria levels and microbial community analyses), presence of PCBs, and PCB-degrading enzymes. Results show that the bay geometry and bathymetry limit the mixing of the extremely high levels of PCBs observed in the eastern portion of the bay. Bay bottom sediments showed the highest levels of PCBs and these sediments were characterized by high organic carbon content and finer grain size. Detectable levels of PCBs were also observed within sediments found along the shore. Microbes from the bay bottom sediments showed a greater relative abundance of microbes from the Chloroflexi, phylum with close phylogenetic associations with known anaerobic PCB-degrading organisms. Based on quantitative PCR measurement of the biphenyl dioxygenase gene, the intertidal sediments showed the greatest potential for aerobic PCB degradation. These results elucidate particular mechanisms of PCB’s fate and transport in coastal, tropical marine environments.

Geometric Design of Bus Bay Based on Vehicle Trajectory Analysis

PURPOSES : It is desirable for buses to be parallel to the face of the bus shelter at a bus stop. In this way, passengers can safely use the buses without moving into the vehicle area. The study was a review of the current bus bay geometric guidelines, to determine whether they lead buses to stop parallel to the face of the bus shelter by analyzing vehicle trajectory. METHODS : A commercial software program for vehicle trajectory analysis was used under our assumptions about bus dimensions and geometric values. The final position of the bus was analyzed for multiple trajectory simulations, reflecting various geometric alternatives. RESULTS : Within the scope of the study, we concluded that the current design guidelines need to be revised by the design values suggested by the study. CONCLUSIONS : The results of the study suggested alternative design values for bus bay geometry, based on the assumption that buses should be parallel to the face of the bus shelter in order to prevent passengers from moving into the vehicle area.

FIELD OBSERVATIONS OF SEICHE EVENTS IN A T-SHAPE BAY

Field observations on secondary oscillations (seiche) in Urauchi Bay of Kami-koshiki Island, Japan were conducted during October 7-21, 2008. The seiches prone bay has a unique configuration as T-shape, which may cause the inherent characteristics of the eigen oscillations. The analyzed data show that the oscillations of the bay have at least two distinct modes; mode-1 oscillation of the period around 25 minutes with forming anti-nodes at the both inward inlets and possessing a node at the bay mouth, mode-2 oscillation of the period around 12 minutes which oscillates between the both inward inlets having the node at the branching point. Next, numerical simulations were conducted to reproduce the secondary oscillations in the bay by providing input sinusoidal waves with the eigen periods of oscillations to the calculating bay geometry. The numerical results are found to show basically consistent characteristics with the field observations.

The role of outflow geometry in the formation of the recirculating bulge region in coastal buoyant outflows

Density-driven coastal currents are a common feature in the world's coastal oceans. These currents may separate from the coastline due to variations in geometry. Past studies have shown that this separation may produce two distinctly different flow states: a continuation of the coastal current, or a recirculating gyre downshelf of, and attached to, the separation point. Laboratory experiments of coastal buoyant outflows (rotationally dominated, buoyancy driven) were undertaken to examine the role of bay geometry on the evolution of the outflow. Experiments were conducted on a rotating turntable in relatively deep water (such that the buoyant layer depth was much less than the total ocean depth). The geometry of the bay-exit was varied, both in exit angle (θ) and in radius of curvature (r c ). The width of the bay was varied such that the bay exit Kelvin number (a ratio between the width of the bay exit and the internal Rossby deformation radius) was order 1 for all experiments. A recirculating bulge (a large, anticyclonic gyre joining the coastal current to the buoyant source) was occasionally observed to form. Results are compared to the Bormans and Garrett (1989) hypothesis: this hypothesis is found to explain a portion of the results only. Geometrical arguments are presented that build upon the Bormans and Garrett hypothesis that parameterizes the magnitude of the flow separation between the buoyant fluid and the exit. A separation ratio, Γ, is defined as a ratio between the inertial turning radius of the flow and the maximum offshore distance between the separated flow and the coast. A recirculating bulge was observed to form for flows with values of Γ > 0.5. The separation ratio, r, is shown to be equivalent to the impact angle, Φ, of the buoyant fluid re-encountering the wall. The impact angle governs the upshelf and downshelf volume flux of the impacting fluid: recirculating bulge formation is found to occur when at least 50% of the source volume flux returns to the source region. This is equivalent to an impact angle greater than or equal to 60-degrees.

Oceanographic and physiographic controls on modern sedimentation within Antarctic fjords

Physical oceanographic data and modern surface sediments were collected from eleven fjords along the western side of the Antarctic Peninsula and South Shetland Islands. Surface sediment samples (62) were analyzed for texture and total organic carbon content. The distribution of biogenic and terrigenous facies within the fjords is controlled by bay geometry and oceanographic regime. Climate plays a secondary role but, along with ice drainage basin size, controls the rate of terrigenous supply to the glacial marine environment. Specifically, fjords along the Danco Coast and Palmer Archipelago with a high length to width ratio tend to have bottom sediments that are arenaceous where ice-rafted sediment is released preferentially at the head of the fjord. Biogenic facies are favored where the bay geometry is complex. Where such complexity exists, separate oceanographic regimes develop that lead to separation of terrigenous and biogenic sediments. Processes of interflow (mid- and deep-water turbid cold tongues) and Coriolis deflection produce terrigenous facies along the inner fjord and western edges of a fjord system. Warm outer bay waters tend to develop a stable eddy circulation pattern that favors the productivity of phytoplankton in the surface layers. Outer bays are therefore floored with organic-rich siliceous muds and ice-rafted material. Only in the South Shetland Islands is melt-water input significant enough to generate estuarine circulation within the fjord, but here strong bottom currents result in arenaceous bottom sediments with no biogenic facies. Ice-rafted diamictons are produced proximal to the edges of small tide-water glaciers in the South Shetlands. The facies relationships established in this study provide a strong reference for paleoclimatic studies that utilize downcore measurements of texture and organic carbon.

Cheniers and chenier plains: A general introduction

Cheniers and chenier plains have been studied in many coastal regions throughout the world. An inventory of the investigations currently being carried out is presented in this and accompanying papers. Cheniers and chenier plains are azonal features. Their distribution ranges from tropical to the subarctic regions and they show a variety of features. Progradational shorelines where mud accretion is temporarily interrupted favour the development of these features. In addition to the concept of Otvos and Price ∗ ∗ 1979. , who define cheniers and chenier plains as being formed exclusively in relation to littoral progradational environments, it is suggested here that chenier formation in deltaic progradational environments should also be included. Genetically, two types of cheniers can be distinguished, depending on the origin of the related sediments: cheniers developing due to wave-winnowing of the muddy sediments and the subsequent concentration of the coarser particles to form a longshore bar or ridge, which is driven shoreward, and cheniers built by littoral drift. In both cases they can be recognised by their sedimentary structures. When cheniers arrive onshore they will migrate further landward due to washover processes under extreme hydrodynamical conditions (e.g., spring tides, storm surges, etc.). To summarise the information concerning the episodic development of chenier plains in order to produce a (or a few) universal model(s) appears to be very difficult owing to the numerous factors that influence their formation. These include river-mouth shifting, sealevel changes, climatic changes, storm frequency, mortality of shellfish and bay geometry. Owing to this sensitivity to environmental changes during their formation, cheniers are considered to be very important geomorphological features. They provide a relatively accurate record of sealevel and environmental changes which can be dated with high resolution.

A Numerical Study of Topographic Wave Reflection in Semi-Infinite Channels

Abstract The Potential vorticity equation describing topographic waves is approximately solved using the channel method of Stocker and Hutter. The domain of integration is a semi-infinite channel and models an estuary, the bathymetry of which is varied through a transverse and a longitudinal topography parameter. It is shown that in this domain the spectrum of topographic waves consists of a discrete and a continuous part. The former exhibits wave modes trapped at the closed end of the channel; these waves correspond to the bay modes in a rectangular basin. Resonances with a similar bay-trapped structure also occur in the continuous spectrum. Their dependence on the bay geometry is studied. A consistent explanation of the three topographic wave types found earlier in an enclosed basin is given in terms of topographic wave reflections.

The Thrust Augmentation of Rocket Motors at High Altitudes

SummaryRocket motors designed for operation in ground launched vehicles generally have nozzle expansion ratios giving optimum thrust at low altitude (about 20 000ft). At higher altitudes the jets are under-expanded and the thrust is less than the maximum available with nozzles of higher expansion ratio. Some of this lost thrust may be regained by suitable design of the propulsion bay geometry, without the low altitude disadvantages of high expansion ratio nozzles. In addition, where the vehicle is propelled by clustered motors, interaction between the jet effluxes at high altitudes can be used to develop an extra thrust acting on the base of the vehicle. The flow changes, from low to high altitude, leading to these effects are described.The results of the first firings of Black Knight drew attention in this country to these effects. Model tests in both the U.K. and America have confirmed them and indicated various means by which the thrust of clustered rockets may be augmented; these are described and consideration is also given to the side effects of thrust augmentation on vehicle control and propulsion bay heating. A full scale experiment, planned for the end of 1962 is outlined and possible future applications are considered.